© 1997 Henrik Nordström

Three basic factors steer all gardening: soil fertility, moisture and timing.

The importance of correct timing in your garden chores cannot be stressed enough. It all begins in the spring. It is never advisable to blindly follow a garden calendar when performing various tasks in the garden, because calendars are based on average years. An average year is simply a mathematical mean year based on several previous years, and does not exist in reality. Every year is thus more or less abnormal.

Soil temperature is the main factor to consider in spring, not air temperature. The soil is very cold after the winter rains, and it takes several sunny days in the upper 60s to low 70s to warm it up to about 60 degrees, which is the optimum temperature for spring planting of e.g. lettuce, spinach, broccoli and carrots. Using a soil thermometer pressed a couple of inches into the ground is very helpful. Germination will be very uneven at lower soil temperatures, and transplants barely grow at all. I rarely make any serious plantings before the beginning of April, except for peas and onion sets which usually can be planted about a month earlier.

Summer crops like tomatoes, cucumbers, squash, beans, corn and peppers need close to 70 degrees in the soil before they are worth planting. At many sites in Seattle, this is not the case until early June. Even then, it is often advisable to cover the corn and bean seed bed with a sheet of clear plastic to raise the soil temperature until the seeds germinate.

Soil moisture is also an important factor. The soil should never be worked when it is too wet, because that will ruin its structure for the whole growing season, causing lumps which are very difficult to break up. If the soil structure is not fine enough, the roots will have difficulty developing and many root crops will not produce at their peak. The soil is ready to be worked when a ball of soil squeezed in your hand falls apart when poked with a finger. When the soil has been loosened and the seedbed prepared, planting should follow immediately. Otherwise, the soil will lose its surface moisture, making seed germination difficult. Watering is never as good as using the soil's natural moisture.

Bare soil looks like an open wound. If the soil is left bare for extended periods, its moisture structure will be distorted, with the top layer being too dry and the deeper layers too wet. Some kind of mulch should therefore be used at all times. In the spring, a sheet of black plastic around the transplants or recently germinated seeds will preserve moisture and raise the soil temperature. As soon as the soil temperature has risen to the optimum level for the vegetable in question, the black plastic should be replaced with a layer of organic mulch, e.g. straw, hay or grass clippings. Woodchips should be avoided in seasonal vegetable gardens, since they tie up the soil's nitrogen while breaking down if mixed into the soil, causing nutrient deficiencies. Placing a layer of newspaper under the mulch will further preserve moisture and also slow down the growth of weeds.

We are fortunate here in Seattle in not usually having to deal with late spring frosts. Some crops will, however, be damaged even if the temperature temporarily drops into the 40s, either in early summer or in fall. A floating row cover (e.g. Reemay or a piece of burlap) can be used to keep the temperature around cold-tender plants like basil a few degrees higher. Clear plastic can be used for cloches and mini-greenhouses, but should not be laid directly on top of the plants, because its heat-preserving capacity is then insignificant.

A few words about watering. Too much watering is the most common mistake gardeners make. A well-prepared, mulched garden bed with established plants rarely needs watering more often than once a week, even in the middle of the summer. A newly seeded bed must be kept constantly moist, but using Reemay to prevent evaporation will cut down on the need for watering. A vegetable garden needs about one inch of water a week. The best time to water is early morning before the sun is hot so that the water will have time to seep into the soil before evaporation occurs. Watering in the evening also prevents evaporation, but does promote diseases and makes a feast for the slugs all night long. You can measure the approximate amount of water applied by placing a number of cans or margarine jars around your plants and making a 1 inch mark inside them.